Humeral nail

ABSTRACT

This nail ( 2 ) comprises a body ( 4 ) that can be inserted into the medullary canal ( 108 ) of the humerus ( 100 ), this body ( 4 ) comprising a proximal part with housing orifices into which interlocking devices ( 22 ) such as screws will be inserted to interlock initially split humeral fragments ( 106   1 - 106   3 ), and a locking device ( 6 ) capable of locking the said interlocking means ( 22 ), this locking device ( 6 ) being free to move relative to the body ( 4 ).  
     The locking device ( 6 ) comprises several openings (6 1 ), each of which comprises a free passage part ( 6   11 ) extending in front of a corresponding orifice ( 4   4 ) in the free passage position, and a locking part ( 6   12 ), the walls of which can stop in contact with a corresponding interlocking device ( 22 ), in the locking position.

This invention relates to a humeral nail.

When a fracture occurs, the proximal part of the humerus can break into several pieces. It is known that these different fragments can be brought together using a humeral nail like that according to the invention.

A nail of this type, for example like that disclosed in U.S. Pat. No. 5,472,444, comprises an elongated body that will be inserted in the medullary canal of the humerus. This body is hollowed out with various drillings, through which screws can pass to mutually interlock the nail and this humeral shaft.

This body is terminated by a proximal end in which at least three orifices are formed, offset at angles from each other. These different orifices house corresponding screws that interlock the different bone fragments that were initially split.

However, this known solution has some disadvantages. Interlocking screws for bone segments tend to become unscrewed, such that their position is modified after implantation, which can cause pain for the patient. Furthermore, if this unscrewing takes place shortly after the surgical operation, consolidation of the humerus assembly may be completely deficient.

To overcome this disadvantage, WO-A-2004/100810 proposes a humeral nail with a main body, different interlocking screws and an internal sheath capable of sliding within the volume inside the body. This sheath has various orifices formed in it, through which the above-mentioned screws can pass.

The first step in placing this nail is to place the sheath inside the body of this nail, and then making the screws penetrate through the various orifices formed in the body and in the sheath respectively. The sheath is then moved along the main axis of the body so as to interlock the screws using the walls of the orifices in the sheath, which stop in contact with the surfaces facing the screws.

However, this alternate solution has disadvantages. In particular, the reliability of the attachment of this nail in the humerus is not always satisfactory.

Having said this, the invention is aimed at proposing a humeral nail capable of overcoming these various disadvantages.

Consequently, its purpose is a humeral nail comprising an elongated body that can be at least partially inserted into the medullary canal of the humerus, this body comprising a proximal part with housing orifices into which interlocking devices such as screws will be inserted to interlock the initially split humeral fragments, this nail also comprising a locking device capable of locking the said interlocking devices, this locking device being free to move relative to the body between a position in which the interlocking devices are free to move, in which this locking device enables free passage of these interlocking means through the said orifices, and a locking position of the interlocking devices in which this locking device locks these interlocking devices relative to the walls of these orifices, characterised in that the locking device comprises several openings, each of which comprises a free passage part extending in front of a corresponding orifice in the free passage position, and a locking part, the walls of which can stop in contact with a corresponding interlocking device, in the locking position.

The invention will be better understood and other advantages will become clearer after reading the following description of an embodiment of a humeral nail according to its principle, given simply as a non-limitative example with reference to the attached drawings in which:

FIG. 1 is an elevation showing a humeral nail according to the invention, once implanted;

FIG. 2 is an exploded elevation showing two different constituents of the humeral nail in FIG. 1;

FIG. 3 is a larger scale elevation showing the orifices and openings in a body and a sheath respectively forming part of the humeral nail in the previous figures, side by side;

FIG. 4 is a perspective view showing an intermediate step in placement of a humeral nail represented in the previous figures; and

FIGS. 5 and 6 are elevations showing part of the body and the sheath forming part of the humeral nail in the previous figures in two different positions, at a different angle from that shown in FIGS. 2 and 3.

FIG. 1 shows a humeral nail according to the invention, denoted as a whole by reference 2. This nail will be used to consolidate a fracture that occurred at a humerus 100 that includes a shaft 102 and a head 104, in a manner known in itself. The initially split fragments 106, to 1063 of this humerus, for which the nail 2 according to the invention is used for consolidation, can also be seen.

As shown particularly in FIG. 2, the nail 2 according to the invention comprises firstly an elongated body 4 with a straight stem shape. This body 4, that will be inserted into the medullar canal 108 of the humerus, is provided with a tapered tip 41 at its distal end. Furthermore, two through holes 42 are formed in its median part, through which screws 20 will pass. These screws interlock this body 4 relative to the humeral shaft 102, in a known manner.

This body 4 is provided with a proximal part 43 opposite the tip 41 which is cylindrical in shape and has a circular cross-section. This proximal part is hollowed out with three through orifices 44 that are circular in shape, and are arranged one vertically in line with each other. These orifices may advantageously be offset at angles from each other in pairs according to the information given in U.S. Pat. No. 5,472,444.

The humeral nail according to the invention also comprises a sheath 6 open at both its ends that is visible particularly in FIG. 3. This sheath 6 that is cylindrical in shape has a slightly greater diameter than the proximal part 43 of the body 4. Thus, this sheath 6 is free to slide around the external surface of this proximal part.

Three through openings 61 pass through the sheath 6, the locations of which correspond approximately to the locations of the orifices 4 ₄. As shown more precisely in FIG. 3 that shows the orifices 4 ₄ and the openings 6 ₁ side by side, the openings have a circular part 6 ₁₁, the diameter of which corresponds approximately to the diameter of the orifices 4 ₄. This circular part 6 ₁₁ is prolonged by an elongated slot 6 ₁₂, the cross-section of which decreases towards the closed end (in other words the upper end) of this slot.

As shown particularly in FIGS. 5 and 6, the sheath 6 is also hollowed out with a notch 6 ₂ that opens up at its lower end in these figures, namely towards the tip 4 ₁ of the body 4. This notch defines two housings 6 ₂₁ and 6 ₂₂ that are oval and circular in shape respectively, separated by a neck 6 ₂₃ with a smaller through dimension. The lower circularly-shaped housing 6 ₂₂ is prolonged by a canal 6 ₂₄ opening up at the lower end of the sheath 6.

Furthermore, the body 4 is provided with a stud 4 ₅ with a substantially circular section with through dimensions globally corresponding to the dimensions of the housings 6 ₂₁ and 6 ₂₂. As will be seen in the following, this stud 4 ₅ can fit selectively into either of these two housings 6 ₂₁ and 6 ₂₂.

Finally, the humeral nail 2 according to the invention comprises a hollow cylindrically-shaped cap 8 with the same diameter as the sheath 6. This cap 8 can be blocked as will be seen in the following, using a screw 10.

Placement of the nail 2 in the humerus 100 described above will now be explained in the following.

The objective is firstly to add the sheath 6 around the proximal part 4 ₃ so that the orifices 4 ₄ coincide with the circular parts 6 ₁₁ of the openings 6 ₁. The assembly formed from this body 4 and this sheath 6 is then inserted into the medullary canal 108 of this humerus 100 in a manner known in itself. As a variant, the body 4 can be inserted into the medullary canal 108 first, and the sheath 6 can then be added around the proximal part 4 ₃. Furthermore, the stud 4 ₅ of the body 4 fits into the lower housing 6 ₂₂ of the notch 6 ₂ formed in the sheath 6, which corresponds to the layout in FIG. 5.

Under these conditions, it is possible to pass interlocking screws 22 through the orifices 4 ₄, the interlocking screws being visible particularly in FIGS. 1 and 4. As is known particularly from U.S. Pat. No. 5,472,444, these screws 22 are used to interlock the initially fractured fragments 106 ₁ to 106 ₃, in order to consolidate them.

The sheath 6 is made to slide relative to the body 4 for example either manually or using an appropriate tool. In the example considered, the objective is to push the sheath 6 towards the distal part 4 ₁ of the body 4, using the cap 8 and the screw 10.

More precisely, the cap 8 is added around the proximal part 4 ₃ of the body 4, the screw 10 is inserted in the inner volume of this cap 8, and this screw is then made to cooperate with an inner thread not shown formed in the proximal part 4 ₃ of the body 4. This screwing of the screw 10 contributes to moving the cap 8 and consequently the sheath 6 along the main axis of the body 4, which is materialised by the arrow F in FIG. 4.

Therefore it can easily be seen that the head 10 ₁ of the screw 10 then forms a stop for the cap 8 such that the cap is immobilised axially relative to the body 4. Consequently, this cap 8 also contributes to axially locking the sheath 6 with respect to this body 4.

When the displacement mentioned above of the sheath 6 with respect to the body 4 is terminated, the circular parts 61, are no longer coincident with the orifices 4 ₄, and the walls of the slots 6 ₁₂ then bear in contact with the surfaces facing the screws 22. The walls of these slots 6 ₁₂ then act as a stop for the screws 22 and prevent any movement of the screws, particularly an unscrewing movement. The circular parts 6 ₁₁ thus form free passage parts for the screws, while the slots 6 ₁₂ form parts locking these screws.

It should be noted that the through dimensions of the circular parts 6 ₁₁ are larger than the dimensions of the screws 22, such that the screws can slide freely. On the other hand, the through dimensions of the slots 6 ₁₂ decrease towards the closed end of each slot. Consequently, when the sheath moves, the walls of these slots 6 ₁₂ cap the surfaces facing the screws 22 so as to lock them and keep them in position.

Furthermore, sliding of the sheath 6 with respect to the body 4 causes displacement of the stud 4 ₅ from the lower housing 6 ₂₂ towards the upper housing 6 ₂₁, which corresponds to the position in FIG. 6. It will be noted that this movement that takes place through the neck 6 ₂₃ is enabled by the nature of the material from which the sheath 6 is made.

It can be imagined that in the position shown in FIG. 6, the sheath 6 is locked with respect to the body 4. The presence of the neck 6 ₂₃ with a small through dimension prevents the stud 4 ₅ from moving back towards the lower housing 6 ₂₂, unless a large force is applied on the sheath 6. Consequently, this measure prevents any unexpected movement of the sheath 6 with respect to the body 4. It should be noted that the screws 6 ₂₂ are not shown in FIG. 6, for reasons of clarity.

The invention is not limited to the example described and shown.

Thus, the sheath 6 extending outside the body 4 can be replaced by a locking device installed free to slide inside this hollow body. This locking device has a smaller diameter and is also provided with openings through which the interlocking screws 22 can be selectively locked.

Furthermore, the slots can extend in different directions from the direction shown. Thus, they can extend the circular parts downwards, obliquely or laterally.

Furthermore, several types of sheaths can be used, the openings of which have different spacings and/or orientations. The most suitable sheath can be chosen for this purpose as a function of the configuration of the bone fragments to be brought together.

Finally, more than one locking notch can be provided to lock the sheath 6 with respect to the body 4, such as 6 ₂ described with reference to FIGS. 5 and 6.

The invention provides a means of achieving the objective mentioned above.

The Applicant realised that the solution described in WO-A-2004/100810 is not very satisfactory, because it does not assure that the interlocking screws are reliably held in position. Thus, these screws are locked by the walls of circular orifices, which necessarily have a larger cross section than the screws since the screws need to slide through these orifices in the free passage position. Under these conditions, the locking force generated by the walls of these orifices is relatively low, such that the screws tend to move away from their initial position.

On the other hand, according to the invention, the sheath 6 reliably locks the interlocking screws 22 which prevents any accidental unscrewing. In this respect, it should be noted that the free passage part of each opening that has large dimensions enables easy sliding of the screws. Furthermore, the different locking parts that are smaller in dimension reliably hold these screws in position. 

1. Humeral nail comprising an elongated body that can be at least partially inserted into the medullary canal of the humerus, this body comprising a proximal part with housing orifices into which interlocking devices such as screws will be inserted to interlock initially split humeral fragments, this nail also comprising a locking device, capable of locking the said interlocking devices, this locking device being free to move relative to the body between a free passage position of the interlocking devices, in which this locking device enables free passage of these interlocking means through the said orifices, and a locking position of the interlocking devices in which this locking device blocks these interlocking devices with respect to the walls of these orifices, characterised in that the locking device comprises different openings, each of which comprises a free passage part extending towards a corresponding orifice in the free passage position, and a locking part, the walls of which can come into abutment with a corresponding interlocking device in the locking position.
 2. Humeral nail according to claim 1, characterised in that the through dimensions of each free passage part are greater than the through dimensions of the interlocking devices, while the through dimensions of locking parts decrease opposite each free passage part such that surfaces facing the interlocking devices are capped and locked in position.
 3. Humeral nail according to claim 2, characterised in that the said orifices are circular in shape and each opening comprises a circular part substantially the same diameter as a corresponding orifice, and a locking slot, the cross-section of which decreases towards the closed end of this slot.
 4. Humeral nail according to claim 1, characterised in that the proximal part, provided with the said housing orifices is cylindrical in shape while the locking device is also cylindrical in shape and has a slightly greater or slightly smaller diameter than the said proximal part such that it can slide relative to this proximal part, inside or outside this proximal part.
 5. Humeral nail according to claim 4, characterised in that this locking device is mobile axially with respect to the proximal part along at least one main axis of this proximal part, between the said free passage position and the said locking position.
 6. Humeral nail according to claim 1, characterised in that this nail also comprises means for moving the locking device towards its locking position, and interlocking this locking device in this locking position.
 7. Humeral nail according to claim 6, characterised in that moving and interlocking means comprise a cylindrical cap capable of coming into abutment with the cylindrical locking device in its locking position, and a device for keeping this cap in contact with this locking device.
 8. Humeral nail according to claim 7, characterised in that the device acting as a stop is a screw, that can penetrate into an inner volume of the cap and cooperate with a tapped thread in the body, a head of this screw keeping the cap in contact with the locking device.
 9. Humeral nail according to claim 1, characterised in that this nail also comprises means for locking the locking means in the locking position, relative to the body.
 10. Humeral nail according to claim 9, characterised in that the interlocking means of the locking device relative to the body comprise a notch formed in this locking device, this notch comprising two housings separated by a neck with a smaller through dimension, these two housings being capable of selectively housing a stud provided on the body. 